After reviewing some recent pictures, I was a little bit concerned that the image quality of the first lens that I bought (a Pentax FA 35mm f2.0 AL), because back then I was obsessed with keeping the lens front element clean, and until I got a UV filter to attach on it, I cleaned it compulsively.
So, is there a real risk of the coating wearing out just by rubbing the lens with microfiber cloths and sometimes using a lens cleaning solution?
Anytime you clean a coated surface on an optical lens you risk damaging the coating. Repeated cleaning, especially if done too vigorously, could eventually wear the coating down.
The good news is that the critical coatings for lenses are those inside the lens that prevent light from bouncing off the back side of an element causing flare or ghosting. In general a UV filter over a front element will cause far more image degradation than wearing off the coating on the front element. The best practice for protecting the front element of your lens is to use a hood, which also contributes to better image quality by reducing glare from off axis light rather than subtracting from it like a flat filter will.
I'm fairly certain any reduction in image quality you are seeing in your pictures is a result of the filter on your lens, not wear to the coating on the front element.
If there is any hard dust particules on the lens, these can scratch the coating and lens itself while rubbing with microfiber cloth.
It is hard to tell about lens cleaning solution, it might harm the coating depending on its ingrediens and the chemical chatacteristics of the lens coating. To be safe, do not use any cleaning solution that uses a solvent other than water.
I take care not to touch the front lens with bare hands and rarely clean them if they do not have fingerprints. The acid and oils in fingerprints are said to damage the lens coatings but I have yet to see an example. Lenspen does a good job of cleaning oily smudges.
I agree with @Michael Clark that UV filters affect the quality of your photographs negatively. I do not use them except from beaches or very dusty environments.
